This invention is generally directed to liquid developer compositions and, more specifically, the present invention relates to a liquid developer containing metal imine bisquinones as a charge adjuvant. More specifically, the present invention relates to liquid developers comprised of metal catechol complexes, such as imine bisquinone metal complexes like the dialkyl complexes, wherein alkyl contains, for example, from 1 to about 20 carbon atoms, like the dibutylcatechol complexes of aluminum, and zinc. The developers of the present invention can be selected for a number of known imaging systems, such as xerographic imaging and printing processes, wherein latent images are rendered visible with the liquid developer illustrated herein. The image quality, solid area coverage and resolution characteristics for developed images usually require, for example, sufficient toner particle electrophoretic mobility. The mobility for effective image development is primarily dependent on the imaging system used. The electrophoretic mobility is directly proportional to the charge on the toner particles and inversely proportional to the viscosity of the liquid developer fluid. For example, a 10 to 30 percent change in fluid viscosity caused, for instance, by a 5.degree. to 15.degree. C. decrease in temperature could result in a decrease in image quality, poor or unacceptable image development and undesirable background development, for example, because of a 5 percent to 23 percent decrease in electrophoretic mobility. Insufficient particle charge can also result in poor transfer of the toner to paper or other final substrates. Poor transfer, for example, can result in poor solid area coverage if insufficient toner is transferred to the final substrate and can also cause image defects such as smears and hollowed fine features. To overcome or minimize such problems, the liquid toners of the present invention were arrived at after extensive research efforts, and which toners result in, for example, sufficient particle charge to transfer and maintain their mobility within the required range of the particular imaging system employed. Other advantages associated with the present invention include increasing the desired negative charge on the developer particles and providing a charge adjuvant, or a charge additive, that is superior to other known charge adjuvants, like aluminum stearate. The aforementioned desired charge can result in improved image development and enhanced transfer.
A latent electrostatic image can be developed with toner particles dispersed in an insulating nonpolar liquid. These dispersed materials are known as liquid toners or liquid developers. A latent electrostatic image may be generated by providing a photoconductive imaging member or layer with a uniform electrostatic charge and subsequently discharging the electrostatic charge by exposing it to a modulated beam of radiant energy. Other methods are also known for forming latent electrostatic images such as, for example, providing a carrier with a dielectric surface and transferring a preformed electrostatic charge to the surface. After the latent image has been formed, the image is developed by colored toner particles dispersed in a nonpolar liquid. The image may then be transferred to a receiver sheet. Also known are ionographic imaging systems.
Typical liquid developers can comprise a thermoplastic resin and a dispersant nonpolar liquid. Generally, a suitable colorant, such as a dye or pigment, is also present in the developer. The colored toner particles are dispersed in a nonpolar liquid which generally has a high volume resistivity in excess of 10.sup.9 ohm-centimeters, a low dielectric constant, for example below 3.0, and a high vapor pressure. Generally, the toner particles are less than 30 .mu.m (microns) average by area size as measured with the Malvern 3600E particle sizer.
Since the formation of proper images depends on the difference of the charge between the toner particles in the liquid developer and the latent electrostatic image to be developed, it is desirable to add a charge director compound and charge adjuvants which increase the magnitude of the charge, such as polyhydroxy compounds, amino alcohols, polybutylene succinimide compounds, aromatic hydrocarbons, metallic soaps, and the like to the liquid developer comprising the thermoplastic resin, the nonpolar liquid and the colorant.
U.S. Pat. No. 5,019,477, the disclosure of which is hereby totally incorporated by reference, discloses a liquid electrostatic developer comprising a nonpolar liquid, thermoplastic resin particles, and a charge director. The ionic or zwitterionic charge directors illustrated may include both negative charge directors such as lecithin, oil-soluble petroleum sulfonate and alkyl succinimide, and positive charge directors such as cobalt and iron naphthanates. The thermoplastic resin particles can comprise a mixture of (1) a polyethylene homopolymer or a copolymer of (i) polyethylene and (ii) acrylic acid, methacrylic acid or alkyl esters thereof, wherein (ii) comprises 0.1 to 20 weight percent of the copolymer; and (2) a random copolymer (iii) selected from the group consisting of vinyl toluene and styrene and (iv) selected from the group consisting of butadiene and acrylate. As the copolymer of polyethylene and methacrylic acid or methacrylic acid alkyl esters, NUCREL.RTM. may be selected.
U.S. Pat. No. 5,030,535 to Drappel et al. discloses a liquid developer composition comprising a liquid vehicle, a charge control additive and toner pigmented particles. The toner particles may contain pigment particles and a resin selected from the group consisting of polyolefins, halogenated polyolefins and mixtures thereof. The liquid developers can be prepared by first dissolving the polymer resin in a liquid vehicle by heating at temperatures of from about 80.degree. C. to about 120.degree. C., adding pigment to the hot polymer solution and attriting the mixture, and then cooling the mixture so that the polymer becomes insoluble in the liquid vehicle, thus forming an insoluble resin layer around the pigment particles.
U.S. Pat. Nos. 3,852,208 and 3,933,664, both to Nagashima et al., disclose colored, light-transparent photoconductive materials which are obtained by a condensation reaction of organic photoconductive substances with reactive colored components. The chemical combination of an organic photoconductive substance having at least one amino or hydroxyl group with a color development component having at least one active halogen atom generates the color developing organic photoconductive materials. Alternatively, the color developing materials can be obtained from the combination of an organic photoconductive substance having at least one active halogen atom with a color developing component having at least one amino or hydroxyl group. The color developing organic photoconductive material may be pulverized in a ball-mill, a roll-mill or an atomizer to produce a toner for use as a dry or wet developing agent, or may be used in combination with other colored substances or vehicle resins.
U.S. Pat. No. 4,524,119 to Luly et al. discloses electrophotographic dry development carriers for use with toner particles wherein the carrier core particles are coated with fluorinated carbon or a fluorinated carbon-containing resin. By varying the fluorine content of the fluorinated carbon, systematic uniform variation of the resistivity properties of the carrier is permitted. Suitable binders for use with the carrier core particles may be selected from known thermoplastics, including fluoropolymers.
U.S. Pat. No. 5,026,621 to Tsubuko et al. discloses a toner for electrophotography which comprises as main components a coloring component and a binder resin which is a block copolymer comprising a functional segment (A) consisting of at least one of a fluoroalkylacryl ester block unit or a fluoroalkyl methacryl ester block unit, and a compatible segment (B) consisting of a fluorine-free vinyl or olefin monomer block unit. The functional segment of block copolymer is oriented to the surface of the block polymer and the compatible segment thereof is oriented to be compatible with other resins and a coloring agent contained in the toner, so that the toner is provided with both liquid-repelling and solvent-soluble properties.
U.S. Pat. No. 4,248,954 to Datta et al. discloses carrier particles for use with a dry toner composition in an electrophotographic process, which are prepared by coating the surface of the carrier particles with a perfluoro carboxylic acid in a polymeric binder. The carrier particles are capable of imparting a positive triboelectric charge to toners.
U.S. Pat. No. 4,268,598 to Leseman et al. discloses a developing powder composition prepared by blending a fluoroaliphatic sulfonamido surface active agent with a desired formulation of toner powder particles. These toners are flowable, finely divided dry powder that are generally colored and are preferably conductive and magnetically attractable.
U.S. Pat. No. 4,139,483 to Williams et al. discloses a finely divided dry toner composition comprising a colorant, a thermoplastic resin, and a surface active additive which is capable of providing a desired polarity and magnitude of triboelectric charging potential to the toner composition. The surface active additives are selected from highly fluorinated materials.
U.S. Pat. No. 4,113,641 to Brana et al. discloses a dry development powder with a high charge to mass ratio comprising a carrier particle treated with a perfluoroalkyl sulfonic acid. The core of the carrier particle can be comprised of a material which will react chemically with perfluoro sulfonic acid, and is preferably a ferromagnetic material such as iron or steel.
U.S. Pat. No. 4,388,396 to Nishibayashi et al. discloses developer particles comprising pigment particles, a binder and an offset-preventing agent selected from the group consisting of aliphatic fluorocarbon compounds and fluorochlorocarbon compounds. Electrical conductivity can be imparted to the developer by causing electrically conductive fine particles to adhere to the surfaces of the particles.
U.S. Pat. No. 4,468,446 to Mikami et al. discloses a dry electrostatographic toner for a pressure fixing process which comprises encapsulated toner particles with a pressure fixable adhesive core material containing a colorant and a pressure rupturable shell enclosing the core material, wherein the outer surface of the shell is an organofluoro compound.
Moreover in U.S. Pat. No. 4,707,429 there are illustrated, for example, liquid developers with an aluminum stearate charge adjuvant. Liquid developers with charge directors are also illustrated in U.S. Pat. No. 5,045,425. Also, stain elimination in consecutive colored liquid toners is illustrated in U.S. Pat. No. 5,069,995. Further, of interest with respect to liquid developers are U.S. Pat. Nos. 5,034,299; 5,066,821 and 5,028,508, the disclosures of which are totally incorporated herein by reference.
In copending patent application U.S. Ser. No. 986,316, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for forming images which comprises (a) generating an electrostatic latent image; (b) contacting the latent image with a developer comprising a colorant and a substantial amount of a vehicle with a melting point of at least about 25.degree. C., said developer having a melting point of at least about 25.degree. C., said contact occurring while the developer is maintained at a temperature at or above its melting point, said developer having a viscosity of no more than about 500 centipoise and a resistivity of no less than about 10.sup.8 ohm-cm at the temperature maintained while the developer is in contact with the latent image; and (c) cooling the developed image to a temperature below its melting point subsequent to development.
The disclosures of each of the patents and the copending patent applications are totally incorporated herein by reference.